A secret Telephone Exchange and ARP / firewatchers post.
What appears to be a Firewatchers / passive defence command bunker.
This lookout post goes down 3 floors underground .Inside are, I think, 6 rooms, the remains of the bottom half of a periscope , light up table and swivel chair, there is also some documentation stuck to the desk regarding local control groups. In another room there is an air pump and escape tunnel on bottom floor.
